<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        span {
            display: inline-block;
            width: 100px;
            height: 100px;
            border: 1px solid #ddd;
            margin: 3px;
            padding: 4px;
        }

        div {
            width: 100px;
            height: 100px;
            /* 边框宽度 */
            /* border-width: 3px; */
            /* 边框颜色 */
            /* border-color: red; */
            /* 
                边框样式
                solid: 实线
                dotted: 点状线
                dashed: 虚线
                double: 双实线
             */
            /* border-style: double; */

            border: 3px double blue;
            /* margin(外边距)上右下左 */
            /* 
                上外边距3px
                右外边距4px
                下外边距5px
                左外边距6px
            */
            
            /* 相对于父级元素水平居中 */
            margin: 0 auto;
            /* margin: 3px 4px 5px 6px; */
            /* margin: 10px;
            margin: 10px 20px; */
            /* padding(内边距) */
            /* 
                上内边距3px
                右内边距4px
                下内边距5px
                左内边距6px
            */
            padding:  3px 4px 5px 6px;
        }
    </style>
</head>
<body>
    <!-- width: 100+2+6+8 -->
    <!-- height: 100+2+6+8 -->
    <span>123</span>

    <div>12312312</div>
</body>
</html>